The size of an ankle effusion following trauma can be used to suggest an underlying fracture. The effusion is measured as follows: Imaginary lines (white) are drawn parallel to the tibial shaft and tangential to the effusion margins at level of ankle joint. Another set of lines are drawn parallel to the first at edge of the articular surface of the tibia (dashed line). The distances between these two sets of lines are added. An ankle effusion >e; 13 mm has a positive predictive value of 80% for
occult fracture and is suggested as a reasonable threshold to prompt additional imaging.
References
Clark TW, Janzen DL, Ho K, Grunfeld A, Connell DG. Detection of radiographically occult ankle fractures following acute trauma: positive predictive value of an ankle effusion. AJR Am J Roentgenol. 1995 May;164(5):1185-9.
The size of an ankle effusion following trauma can be used to suggest an underlying fracture. The effusion is measured as follows: Imaginary lines (white) are drawn parallel to the tibial shaft and tangential to the effusion margins at level of ankle joint. Another set of lines are drawn parallel to the first at edge of the articular surface of the tibia (dashed line). The distances between these two sets of lines are added. An ankle effusion >e; 13 mm has a positive predictive value of 80% for
occult fracture and is suggested as a reasonable threshold to prompt additional imaging.
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